1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method, and in particular relates to an electrophotographic image forming apparatus and an electrophotographic image forming method.
2. Description of the Related Art
In an electrophotographic image forming apparatus, an image is formed using static electricity and thus the image density, line width, and print position of an image fluctuate due to a fluctuation in environmental conditions such as temperature and humidity, in the use environment of the apparatus, and due to a temporal degradation of a photoreceptor, a developer or the like, that is, due to the changes in durability, and thus a stable image formation cannot be carried out.
In order to prevent this problem, a control (hereinafter, referred to as “image stabilization control”) is carried out, in which the information about environmental conditions, the information about durability, and the information about an image-adjusting pattern image are detected and fed back to conditions for forming an image (hereinafter, referred to as “image forming conditions”), thereby stabilizing the image to be formed (e.g., see Patent Literature 1). Here, the “image-adjusting pattern image” is a pattern image exclusively formed for adjusting an image. By carrying out this image stabilization control, an image can be stably formed even if there are factors destabilizing the image formation.
As the above-described image stabilization control, generally two methods are known. One of them is a method (hereinafter, referred to as an “image stabilization control method (1)”), in which by means of a toner density sensor installed on an opposing portion of an intermediate transfer belt, there is detected the toner density of an unfixed image-adjusting pattern image formed on the intermediate transfer belt. The other one is a method (hereinafter, referred to as an “image stabilization control method (2)”), in which by means of a toner density sensor installed in a paper transport section after a fixing unit, the toner density of an image-adjusting pattern image fixed to a paper is detected.
For a relatively inexpensive image forming apparatus, the image stabilization control method (1) is often adopted. However, in the case of the stabilization control method (1), since the toner density sensor is installed downstream of a secondary transfer unit so as to face an intermediate transfer belt, it is not possible to detect fluctuations generated in the secondary transfer unit or in the fixing unit and to feedback the same to an image forming condition. Because these fluctuations are controlled by prediction, the stabilization control method (1) has a disadvantage of lacking the stability of image quality.
In contrast, a relatively expensive image forming apparatus, the image stabilization control method (2) has been adopted in recent years. In the case of the image-stabilization-control method (2), since the fluctuations generated in the secondary transfer unit or in the fixing unit, which cannot be detected by the image stabilization control method (1), can be also detected and fed back to an image forming condition, a further increase in image quality can be achieved as compared with the image stabilization control method (1).
Patent Literature 1: Japanese Patent Laid-Open No. 2006-39036